Kudos for safeguarding DD by taking her to your mother’s.
You’ve previously written about H’s refusal to parent his children, as well as his abuse and neglect of DD. His current refusal to acknowledge her is more of the same.
It was sickening to read about her world book day, when she was excited about being in her costume/makeup for her Zoom class. After you left for work, she couldn’t get her Zoom to work, but her monster father wouldn’t help with it. He then took a photo of her distressed face, put it on the family WhatsApp, and thought it was funny. Such heinous cruelty is unforgivable. The damage being done to this child is monumental.
Both children are being mistreated. DD is his main target, but DS should not be responsible for his sister’s sole care when you are absent. Isn’t there also a 3rd child?
You’ve also had a thread about H’s refusal to help with any messy chores, including cleaning the bathrooms, emptying bins, or cleaning up after the family dog when he (doggie) was ill. H would actually leave urine, feces and vomit on the carpet for you to clean up because it was beneath him.
You are essentially a single mother, and your children are learning a toxic relationship model.
I hope that you will take steps to divorce this sadistic abuser and can move to a home with enough space for everyone. DS needs to be with the parent who actually cares.